The present invention relates to an integrated process to upgrade relatively low-value paraffinic materials to high-octane gasoline and high-cetane diesel. The process is particularly applicable to the upgrading of low-value paraffinic feeds, such as iso-butane and heavy virgin naphtha to make high-octane alkylate and high-cetane diesel via oxidation.
Alkylate is composed of a mixture of high-octane, branched-chain paraffinic hydrocarbons (mostly iso-heptane and iso-octane). Alkylate is a premium gasoline blending stock because it has exceptional antiknock properties, relatively low Reid Vapor Pressure (RVP), and is clean burning. The octane number of an alkylate depends mainly upon the kind of feeds used and upon operating conditions. For example, iso-octane results from combining C4 olefins with iso-butane and has an octane rating of 100 by definition. There are other products in the alkylate, so the octane rating will vary accordingly. Current technologies for producing high octane alkylate require C4 olefins, particularly iso-butylene, which are alkylated with iso-butane using an acid catalyst, such as H2SO4, HF, or solid acids as zeolites. When C4 olefins are constrained, expensive on-purpose C4 olefin generation is utilized to provide feedstock, and requires high temperatures, low pressures, and frequent catalyst regeneration. There remains a need to develop a new process for utilizing abundant paraffins, specifically iso-butane, to produce high-octane alkylate without expensive C4 olefin as a feedstock.
High-cetane diesel (diesel with a cetane number in the range of about 40-110, preferably about 45-90, and more preferably about 50-80) is typically obtained from crude distillation, or from Fischer-Tropsch synthesis. These diesel molecules, particularly those from Fischer-Tropsch synthesis, require an additional hydro-isomerization (i.e. dewaxing) step to meet the cloud point specification for diesel. Low octane naphtha, such as heavy virgin naphtha, is typically converted to aromatics, a high octane gasoline blend, using catalytic reforming. There remains a need to utilize abundant naphthas, such as heavy virgin naphtha, heavy cat naphtha, and coker naphtha, to produce high-cetane diesel, a more carbon-efficient disposition for heavy virgin naphtha than gasoline.
Demand for high-octane gasoline and high-cetane diesel is expected to grow. Additionally, the increased supply of light paraffins in North America and the abundance of heavy virgin naptha creates a need and opportunities for upgrading to high-octane gasoline and high-cetane diesel. Disclosed herein is an integrated process for achieving both.